1. Field of the Invention
The present invention relates to an inkjet printing apparatus and an inkjet printing method for discharging ink from nozzle arrays of printheads for printing.
2. Description of the Related Art
Inkjet printing apparatuses which print on various recording media by discharging ink are capable of high-density, high-speed printing operation. Also, the inkjet printing scheme has many advantages including low running costs and low noise during printing operation. Consequently, inkjet printing apparatuses have been commercialized and used as stationary printers, portable printers, or other peripheral devices for various purposes.
Known printing schemes for inkjet printing apparatuses include the so-called serial printing scheme in which a carriage which carries a printhead and ink tank scans over a recording medium, discharges ink from nozzle arrays of the printhead, and thereby prints on the scanned area. In this scheme, the recording medium is fed by a predetermined amount in a direction (sub-scanning direction or transport direction) approximately orthogonal to the carriage scan direction (main scanning direction) between scans by the carriage. This scheme prints on the entire recording medium by repeating carriage scans and feeding the recording medium. Another known scheme is the so-called full-line printing scheme. This scheme performs printing by conveying a recording medium relative to a printhead in which discharge nozzles are arranged in a range which corresponds to the width of the recording medium.
Recently, a large number of inkjet printing apparatus with various advantages such as described above have been provided as products which perform color printing using multiple colors of ink. In such inkjet printing apparatuses, generally black ink is used frequently to print characters and the like. Consequently, sharpness, clearness, and high density of printed characters are required of the black ink. For that, there is a known technique which lowers permeation of black ink into printing media and thereby inhibiting coloring matter such as dyes and pigments in the black ink from permeating into the recording media. This increases the amount of coloring matter which remains fixed on the recording media and thereby increases the sharpness and density of printed images.
However, the use of black ink with reduced permeation into recording media may lead to problems such as those described below. Specifically, if the discharge amount of ink droplets is increased to increase the printing density of characters and the like printed in black ink, the ink can bleed in edge portions of the characters. Also, in an image in which black and color areas are placed adjacent to each other, black ink does not permeate the recording medium quickly because of its low permeation and may get mixed with color ink across borders between the areas. This can cause bleeding (deterioration of printing quality due to mixing of inks) on boundaries between the black and color areas.
Thus, Japanese Patent Laid-Open Application No. 05-278221 proposes a method which detects edge portions and non-edge portions in character data and the like to be printed in black ink, reduces the ink discharge amount in the non-edge portions, and thereby improves smear resistance and fixing characteristic while maintaining sharpness of printed characters and the like.